negbin1 {spaMM} | R Documentation |
Alternative negative-binomial family
Description
Returns a family
object suitable as a fitme
argument for fitting negative-binomial models with variance linearly (affinely) related to the mean : variance=
/shape, where the shape parameter need or need not be specified, depending on usage.
The model described by such a family is characterized by a linear predictor, a link function, and such a negative-binomial model for the residual variation. The zero-truncated variant of this family is also handled.
A fixed-effect residual-dispersion model can be fitted, using the resid.model
argument, which is used to specify the form of the logarithm of the shape parameter. Thus the variance of the response become /
exp(<specified linear expression>)
.
Usage
negbin1(shape = stop("negbin1's 'shape' must be specified"), link = "log", trunc = -1L)
Arguments
shape |
Parameter controlling the mean-variance relationship of the |
link |
log, sqrt or identity link, specified by any of the available ways for GLM links (name, character string, one-element character vector, or object of class |
trunc |
Either |
Details
The name NB_shape
should be used to set values of shape in optimization control arguments of the fitting functions (e.g., fitme(.,init=list(NB_shape=1))
); but fixed values are set by the shape
argument.
The family should not be used as a glm
argument as the results would not be correct.
Value
A list, formally of class c("LLF", "family")
. See LL-family
for details about the structure and usage of such objects.
See Also
Examples in LL-family
. resid.model
for an example with a residual-dispersion model.